(1) Field of the Invention
The present invention relates to a scope using a multifilament type plastic optical fiber as an image-transmitting member. More particularly, the present invention relates to an endoscope which makes it possible to observe an object in the dark field of vision as a bright and sharp image and shows a good handling property, such as an esophagoscope, a gastrocamera, an intestine endoscope, a bronchoscope, and endoscope exclusive for a specific organ, or a blood vessel endoscope.
(2) Description of the Related Art
A fiber scope comprising an image-transmitting member composed of an image-transmitting optical fiber bundle comprising a great number of bundled fine glass type optical filaments having a diameter of about 10 to about 50.mu. and a light-transmitting member composed of a plurality of optical filaments having a larger diameter, is known and disclosed in, for example, Japanese Unexamined Patent Publication No. 59-155231.
However, the known endoscope of this type is defective in the following points. Namely, the image-transmitting optical fiber bundle is formed by arranging several hundreds of quartz type optical filaments, which are very fine, rigid, and easily broken and have a poor handling property, so that the same positional relationship is maintained on both end faces of the image-transmitting optical fiber bundle, and therefore, it is very difficult to prepare this image-transmitting fiber bundle without breaking some of the fine quartz filaments, because of their poor handling property. Accordingly, the manufacturing cost is greatly increased. Furthermore, if even one of several hundreds of thus arranged quartz type optical filaments is broken, transmission of an image becomes impossible. Therefore, close attention should be paid when an endoscope is assembled by using this quartz type optical fiber and while the assembled endoscope is being used. When a break occurs, repair is very difficult and maintenance requires much labor. Moreover, the quartz type multifilament optical fiber bundle is rigid and has a poor handling property, and this poor handling property is a serious problem in case of a medical endoscope used for observing the interior of a fine tubule. Furthermore, this rigid optical fiber bundle causes pain to a patient during the observation. In order to improve the poor handling property and moderate the pain felt by a patient, the development of a material for a fiber scope having a good flexibility and softness is desired.
Still further, in the conventional endoscope fabricated by using the glass type optical fiber, the ratio of the area occupied by the core acting as a light-transmitting member in the cross-section of the optical fiber bundle is small, and the conventional endoscope is still unsatisfactory in that an object present in the dark field of vision cannot be observed as a bright and sharp image.